mnttab(4) File Formats mnttab(4)NAMEmnttab - mounted file system table
DESCRIPTION
The file /etc/mnttab is really a file system that provides read-only
access to the table of mounted file systems for the current host.
/etc/mnttab is read by programs using the routines described in getmn‐
tent(3C). Mounting a file system adds an entry to this table. Unmount‐
ing removes an entry from this table. Remounting a file system causes
the information in the mounted file system table to be updated to
reflect any changes caused by the remount. The list is maintained by
the kernel in order of mount time. That is, the first mounted file sys‐
tem is first in the list and the most recently mounted file system is
last. When mounted on a mount point the file system appears as a regu‐
lar file containing the current mnttab information.
Each entry is a line of fields separated by TABs in the form:
special mount_point fstype options time
where:
special The name of the resource that has been mounted.
mount_point The pathname of the directory on which the filesystem is
mounted.
fstype The file system type of the mounted file system.
options The mount options. See respective mount file system man
page in the section below.
time The time at which the file system was mounted.
Examples of entries for the special field include the pathname of a
block-special device, the name of a remote file system in the form of
host:pathname, or the name of a swap file, for example, a file made
with mkfile(1M).
IOCTLS
The following ioctl(2) calls are supported:
MNTIOC_NMNTS Returns the count of mounted resources in the cur‐
rent snapshot in the uint32_t pointed to by arg.
MNTIOC_GETDEVLIST Returns an array of uint32_t's that is twice as
long as the length returned by MNTIOC_NMNTS. Each
pair of numbers is the major and minor device num‐
ber for the file system at the corresponding line
in the current /etc/mnttab snapshot. arg points to
the memory buffer to receive the device number
information.
MNTIOC_SETTAG Sets a tag word into the options list for a
mounted file system. A tag is a notation that will
appear in the options string of a mounted file
system but it is not recognized or interpreted by
the file system code. arg points to a filled in
mnttagdesc structure, as shown in the following
example:
uint_t mtd_major; /* major number for mounted fs */
uint_t mtd_minor; /* minor number for mounted fs */
char *mtd_mntpt; /* mount point of file system */
char *mtd_tag; /* tag to set/clear */
If the tag already exists then it is marked as set
but not re-added. Tags can be at most
MAX_MNTOPT_TAG long.
Use of this ioctl is restricted to processes with
the {PRIV_SYS_MOUNT} privilege.
MNTIOC_CLRTAG Marks a tag in the options list for a mounted file
system as not set. arg points to the same struc‐
ture as MNTIOC_SETTAG, which identifies the file
system and tag to be cleared.
Use of this ioctl is restricted to processes with
the {PRIV_SYS_MOUNT} privilege.
ERRORS
EFAULT The arg pointer in an MNTIOC_ ioctl call pointed to an
inaccessible memory location or a character pointer in
a mnttagdesc structure pointed to an inaccessible mem‐
ory location.
EINVAL The tag specified in a MNTIOC_SETTAG call already
exists as a file system option, or the tag specified in
a MNTIOC_CLRTAG call does not exist.
ENAMETOOLONG The tag specified in a MNTIOC_SETTAG call is too long
or the tag would make the total length of the option
string for the mounted file system too long.
EPERM The calling process does not have {PRIV_SYS_MOUNT}
privilege and either a MNTIOC_SETTAG or MNTIOC_CLRTAG
call was made.
FILES
/etc/mnttab Usual mount point for mnttab file system
/usr/include/sys/mntio.h Header file that contains IOCTL definitions
SEE ALSOmkfile(1M), mount_cachefs(1M), mount_hsfs(1M), mount_nfs(1M),
mount_pcfs(1M), mount_ufs(1M), mount(1M), ioctl(2), read(2), poll(2),
stat(2), getmntent(3C)WARNINGS
The mnttab file system provides the previously undocumented dev=xxx
option in the option string for each mounted file system. This is pro‐
vided for legacy applications that might have been using the dev=infor‐
mation option.
Using dev=option in applications is strongly discouraged. The device
number string represents a 32-bit quantity and might not contain cor‐
rect information in 64-bit environments.
Applications requiring device number information for mounted file sys‐
tems should use the getextmntent(3C) interface, which functions prop‐
erly in either 32- or 64-bit environments.
NOTES
The snapshot of the mnttab information is taken any time a read(2) is
performed at offset 0 (the beginning) of the mnttab file. The file mod‐
ification time returned by stat(2) for the mnttab file is the time of
the last change to mounted file system information. A poll(2) system
call requesting a POLLRDBAND event can be used to block and wait for
the system's mounted file system information to be different from the
most recent snapshot since the mnttab file was opened.
SunOS 5.10 20 Dec 2003 mnttab(4)
